???????????????????????????????
????????????????*.h?????
???????????????*.cpp?????
???????????????????????????
??????????????????????????Clock.h??Clock.cpp??main.cpp
???????????????Clock.h??Clock.cpp????????Clock.obj????main.cpp??Clock.h????????main.obj???????????????Clock.obj??main.obj????????main.exe??????????
????#include <?????>
???????????д?????????C++???????include?????????<>?б???????????????????????????????
????#include "?????"
???????????д????????????????????????????????""?б????????????????????????????????